Method and means for controlling the moisture content of paper or other material



. H. L. BONE 1,722,655 METHOD AND MEANS FOR CONTROLLING THE MOISTURE CONTENT OF PAPER OR OTHER MATERIAL 2 Sheets-Sheet 1 Jul so, 1929.

Filed 000. 24, 1927 July 30, 1929. H BQNE- 1,722,655

METHOD AND MEANS FOR CONTROLLING THE uoIsTUnE CONTENT OF PAPER OR OTHER MATERIAL Filed Oct. 24; 1927 2 Sheets-Sheet 2 Patented July 30, 1929.

UNITED STATES PATENT OFFICE.

HERBERT L. BONE, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR T0 ATLANTIC PRE- CISION COMPANY, OF BOSTON, MASSACHUSETTS, A CORPORATION OF MASSACHU- SETTS.

METHOD AND means Leon CONTROLLING THE morsrunn con'rnu'r or PAPER on.

, DTHEB MATERIAL.

Application filed October 24, 1927. Serial No. 2281219.

, 5 is desirable, such for example, as in the manufacture of paper. While all of the various constituents of the Web of paper should be maintained uniform and the present invention in its broader aspects is not limited to any 10 one, this invention more specifically relates to the control of the moisture content of paper or other continuously manufactured or treat-- ed product.

. The nature of this invention will be better one particular example illustrating the general problem with which it has to do and showing its more specific adaptation to theautomatic control of moisture content of paper. Assuming, therefore, that moisture content only is to be controlled. and that the material is coming off from a drier, the drying action of which is dependent in amount upon the amount-of steam supplied thereto for heating drying elements, 1f the steam controlling valve is set at just the proper amount to deliver the material at exactly the desired moisture content, nothing happens. If now conditions change so that the moisture content departs somewhat from that desired, the steam valve is actuated automatically in a corrective manner, small moisture deviations requiring small valve corrections and large deviations requiring correspondingly larger valve corrections. A suitably a justed proportionality between steam valve ,response and moisture deviation is suflicient alone to hold the moisture between more or less close limits, but is subject to an inherent error in that except for hand adjustments, one position of the valve can be had only through one corresponding moisture content so that valve adjustments inv'olve changes in moisture setting of the instrument, ossibly small, but certainly undesirable.

where it is not possible or convenientto employ a positive mechanical connection between the moisture indicator and the valve, as is usually the case. there is certain to be a drifting, because of im erfect synchronism, of the correspondence getween a particular indication and a particular valve setting. As

i a resu t the in trument may, articularly understood by considering at greater length oreover,.

after an extended time ofoperation with its cumulation of errors, tend to hold the mois ture content at a diflerent value from that deslred and for which the instrument was initially ad usted. Where fluctuations of drying requlrements are unusually wide or erratic, it becomes necessary to deal with wide instead of narrow ranges of steam valve position and with large instead of small changes in the temperature of the heavy masses of the driers,

entailing large time lags and considerable tendencies to overrun the temperatures at the workmg faces of the drying mechanism and consequent degree of dryness aimed countof accumulative effects and irregular distr bution of temperatures during what may be termed thermal acceleration and de celera-tion. With such severe conditions a simple proportionality between instrument responses to changes from normal and displacement of the steam valve controlled thereby from its normal, is not in itself enough to give the best regulation of moisture of which the method is capable and under such conditions also the drifting tendency is much increased.

The present invention, therefore, has to do with modifications and refinement which are particularly adapted to deal with such extreme conditions as well as with less severe conditions morder to obtain the closest sible regulation. To this endl provi e a controlling instrument which, no matter what its correcting motions may he, acts or tends to act to return the corrective portion of the mechanism to a position corresponding to that where the material has exactly the desired moisture content Ilesired and quite irrespective of any particular valve, setting. For the purpose of lllustration only, and not of restriction, the invention is shown herein as applied to an automatic moisture control ling mechanism for a paper machine, the mechanism being of a type more particularly described and claimed in an application for patent by Albert Allen and John G. Callan,

erial, No. 228,220 filed October 24, 1927, for apparatus for controlling moisture content of paper or the like, and which is shown'in the accompanying drawings.

Referring to these drawings,

Figure 1 is a somewhat diagrammatic view showing a portionof a paper drier and a at, on ac-.

mediately following the last drier.

calender stack with automatic mechanism for controlling the steam supply to the drier.

Figure 2 is an elevation of a steam valve mechanism, the casing cover being removed.

Figure 3 is a section on line 3-3 of Figure 2. I

Figure 4 is a detail shown in Figure 3 but drawn to a larger scale.

Figure 5 is a somewhat diagrammatic perspective of a control mechanism for the valveactuating mechanism.

Figure 6 is a section through the hygrometric device.

Figure 7 is a Wiring diagram. Referring first to Figure 1, A represents a part of the usual drier stack for the paper machine, being either the last portion of the main stack for a machine without means for top sizing,or the last of the small stack beyond the size tub in machines so equipped. At B is shown a calender im- The paper coming from the calender B passes in responsive relation to a hygrometrio device shown in detail in Figure 6 at C, as shown this device having a hygrometric element responsive to the moisture of the paper after it leaves the calender. It might, however, be placed in responsive relation "to the paper after its initial drying and before it is passed through the top size tub in the production of top sized papers, or it might be placed at any point in the pa er machine, paper-coating machine, or the like, at which the paper or other material should have a determinate moisture content arising from, or residual from, thermally controllable processes or operations preceding the measuring point.

The hygrometer C is shown as connected to an instrument D which contains parts of certain high frequency circuits as shown diagrammatically in Figure 7. In a portion of these circuits is placed a recording and controlling instrument E shown in detail in Figure 5 and there may also be in these circuits an indicating instrument F of the thermoammeter type. The instrument E controls the supply of electrical energy to a valveactuating and'controlling mechanism at H which is shown in detail in Figures 2, 3 and 4. v

The hygrometric device may be of any suitable type, but as herein shown more particularly in Figure 6 is that described and claimed in the application for patent of Albert Allen, Serial No. 152,126, filed December 2, 1926, for hygrometers. prises an open sidedelongated box orcasin 10 having at one end an enlarged boxrshape portion 11 in which are positioned the plates 12 and 13 of a book type electrical condenser. As shown the plate 12 is supported from an insulatin sheet 14 fixed in a portion of the box and t e plate 13 is provided with a knife It comedge bearing portion 15. The knife edge portion 15 is held to its bearing 16 as by means of one or more springs 17 and it is normally held rocked toward the plate 12 as by means of thespring 18. An adjustable stop screw 20 is shown as threaded through the end portion of the-box,-shapedportion 11 and passes through suitable holes through the late 12 and theinsulation 14, its inner end serving to limit the approach of the plate 13 toward'the late 12.- The edge of the plate 13 remote rom the knife edge 15 and adjacent to the open side of the container 10 has fixed thereto as at 21 one end of a hygrometric ribbon 22. This ribbon maybe'of any suitable form, one which has been found satisfactory in service being made of artificial silk as by the viscose process. The opposite end of the ribbon passes about a fixed rod 24, about a rod 25 which is adjustside of the open sided portion. When so constructed the paper may be passed over the device without actuallycontacting therewith and yet enclose a body of air circulated by the movement of the paper in intimate contact with the paper surface and the hygrometric material so as to produce the de' sired response in the hygrometric material in apparently as satisfactory a manner as where the paper is drawn over the hygrometric device in contact with the casing.

Changes in the moisture content of the paper passing over this device cause corresponding proportional changes in the mois ture content and consequently in the Ian th of the ribbon, thus changing the spacing netween the condenser plates 12 and 13 and changing the capacity of the condenser formed by these plates. The sensitivity of this device may be regulated by adjusting the initial spacing between the condenser plates, the further the plates are initially placed, the less sensitive being the indication, as an equal movement of the plate 21 under such circumstances causes less change in capacity than where the plates are closer together. It will thus be seen that the moisture content of the paper passing over the hygrometric device controls the capacity of the condenser. This capacity and changes of capacity may be accurately and promptly recognized by suitable apparatus, such for example as that disclosed in the Allen application for patent Serial No. 166,705, filed February 8, 1927, for

- means for measuring characteristics of material.

An apparatus of this general type is disclosed somewhat diagrammatically in. the

" pressed on the transformer 31. The second-9 wiring diagram of Figure 7 which includes the instruments D, F and E. The particular circuits shown in this Figure 7 are disclosed method of compensating for voltage changes impressed thereon. In general, it may be stated here that theycomprise a primary oscillatory circuit indicated at M coupled as by the capacity coupling 30 with a secondary p oscillatory circuit-N. The primary oscillatory circuit is shown as energized through a transformer 31 from an alternating current source and contains an electron tube 32, to-

gether with various canacitances and induct ances so placed that the'circuit M oscillates at a desired frequency. Any suitable oscillatory circuit can be used. but that shown is particularly suitable for the purpose, in that it may be made to inherently compensate for quite considerable changes of voltage "imary circuit N is provided with'capacitances and inductances and includes as'a part of the capacitance that represented by the hygrometrically controlled condenser plates 12 and 13. It is so adjusted relative to the primary circuit M that its free period of oscillation is slightly higher than that of the primary circuit-M, but is sufliciently near resonance therewith so that acurrent flow is induced therein dependent in amount on its nearness to resonance with the primary circuit M. Under such conditions the changes in capacis tances of the plates 12 and 13 bring the natural period of the secondarycircuit closer 'to or farther from resonan'cein accordance with the changes of spacing between the plates due to moisture changes in the ribbon and vary the current flow in the secondary circuit correspondingly. These changes in current flow may be recognized, as by means of the thermo-ammeter Fjtheparts being so arranged as more fully disclosed in the Allen application Serial No. 166,705 that amidpositionon the scale of the thermo-ammeter indicates a desired condition, which in the present instance represents a predetermined moisture content of the sheet material.

. Supplementary to, or used in place of the thermo-ammeter F, is the instrument E shown in detail in Figurev5, to which currentin amount dependent on the moisture response of the hygrometric device 'is conducted through the wires 40 and 41. These wires lead toa mini-voltmeter of the well known dArsonval type "having a needle .50 carried by a moving element 51 mounted in a familiarmanner between the poles of the permanent magnet 52. The current thus causes de'-' ,flectionof the needle in proportion to the moisturecontent of the material, theappara- 'tus beingiso adjusted that the needle 50 takes a inidscalerpositio'n when the response of the ployedfor this purpose I pointer 50 ofi' scale in either direction. This m'illi-voltmeter apparatus is used to control .a cur-rent supply to a relay at G in such a ma er as to control the valve-actuating mec ianism at H, as will later more fully apear.

Usually besides serving as an indicator of moisture content, the instrument E will also be so designed as to record the moisture content and the/instrument herein illustrated is adapted, for both purposes. 4 For the purpose of recording, as well as. for actuating the mechanism H, means are provided for depressing the needle 50 at suitable time intervals. For this purpose an arcuate depressor bar 55 is shown which bears upon a conical ,roller 56 preferably of light, thin silver, on an insulating wire, which is journaled on the needle 50 but insulated from it.

This depressor bar 55 is carried by a parallel motion mechanism so as to move. vertically in a direction parallel with the swinging axis of the needle. Forthispurpose a shaft 57 is 'journaled in suitable standards at the back of the instrument and has fixed thereto 'adj acent to, opposite ends, arms v58 and59. Pivoted at points beneath the arms 58 and 59 and in vertical alinement with the shaft 57 are,

' similar arms 60 and 61 The forward ends of the arms 58 and 60 an d 59 and 61, respectively. are pivot-ally con ected to the brackets 62'and 63, respectively, to which opposite ends of the depressor bar 55 are fixed; At suitable time intervals the shaft 57 is rocked to move the depressor bar downwardly and then upwardly. For this purpose the shaft 57 is proifided with a crank arm 65, connected through a link 66 to a suitable actuating cam 68 of a 'mechanism at 67, herein shown as a synchronous electric motor clock of any suitable type.

1 Beneath the needle 50 is shown positioned a recording paper sheet or strip 70 which passes over. a suitable driving roll 71 and beneath a ribbon 72, preferably of carlon paper, which passes about end rollsbeyon op osite edges of the paper 70, one of these rolls eing shown at 73. This roll 71 is rotated slow to' effect a progressive feed of the record s set and for this purpose it is shown as fixed to a shaft 74 having a sprocket wheel 75 thereon which may be driven as-by means of a chain a 76 from the clock motor. 67. V In order that a fresh part of: the surface {or the carbon paper may be presented beneath the. needle at each printingactuation thereof, the roller 73 over which the carbon strip passes is shown'as connected for rotation by the shaft 74, spiral gears 77 and 78 on the shaftJ i and the shaft 79 whichcarry the roll 73 being shown vas em- It is desirable that the needle 50 be given a quick downward motion so that it may strike upon the carbon paper a sharp quick blow in order to produce the desired mark on the record sheet and then relieve the needle from contact with either bar or paper. For this purpose means are provided for snapping the needle downwardly to make a sharp blow and then retract it somewhat from the carbon paper, even though the depressor bar may be holding the roll 56in its downward position after the recording blow has been struck. For this purpose the bar 58 has pivoted thereon a bell crank lever 80. One arm of this lever, as 81, is connected through a spring 82 to a bar 83 which is positionedabove the needle 50 forwardly of the depressor bar 55. A spring 85 acting on the arm 84 of the lever holds a pin 86 on the lower end of this arm against the teeth of a ratchet wheel 87 which is held from'rotation in one direction by a springpressed pawl As the bar 58 is swung downwardly to depress the depressor bar the pin 86, riding on the inclined face of one of the teeth of the ratchet wheel 87 moves or holds the arm 81 upward until such time as the pin 86 rides over the apex of the ratchet tooth, whereupon the spring 85 immediately acts to snap the lower end of the arm 84rearwardly, this sharply depressing the arm 81 and bringing the bar 83 down on the needle 50 with a sharp blow. The inertia of the bar 83 is sufficient to produce an overthrow to an extent sufficient to cause the needle to strike a sharp blow on the printing'strip and the record paper, the spring 82 then acting to lift the bar 83 slightly so that the needlet50 may retract from the carbon ribbon and the bar 83 from the needle. It should be understood, of'course, that the bar 83 has a similar actuating mechanism on each end.

When the depressor bar moves the needle 50 downwardly, it brings the roller 56 down on to a sector member 850. This member carrieson its upper face an arcuate, conducting strip 860 extending its entire circumference and a pair of arcuate conductor strips 870 and 880 parallel tothe strip 860 and spaced apart centrally. As the-roller 56 is brought down, therefore, it makes contact with the strip 860 in whatever angular position the needle 50 may be. "If it is in the central position, it comes down between the strips 870 and 880 and makes contact with neither. If, however, the needle when it is depressed is away from the central position and thus denotes departure from the desired moisture content of the paper, it connects electrically the contact of the strip 860 with one or the other of the strips 870 and 880. When the' contact is made between the strips 860 and 870 electrical connections are made through the'relay G to the valve-actuating mechanism H, as will later appear, in a manner to decrease the heating effect of-the drier, but

when the contact is made between the strips 860 and 880, the mechanism H is operated in the reverse direction to increase vthe heating effect of the drier.

The control of the valve-actuating mechanism is designed to be effected whenever the needle moves away from its central or normal position and is depressed, and is so de signed that proportionality betweent the deflection of the needle from this central position and the valve response is secured, this proportionality being effected bya followup mechanism. The follow-up mechanism illustrated is as follows: The segment 850 .97. This spider is j'ournaled at opposite ends on the shafts 91' and 93. This particular connection between the .shafts 93 and 91 is for a purpose which will presently be described. The follow-up mechanism isfactuated by rotation of the spider 97 which through the rotation of the pinions 95 and 96 by their engagement with the gear 94, turns the gear 92 and rotates the shaft 91. This rotation of the spider is accomplished by means of ,a sprocket wheel 100 carried by the spider and which is connected through a chain 101 with a reversing clock motor 102. As shown this clock motor has a wire 103 connected to one side of the single phase alternating current supply and two field terminal wires 104,105. The motor causing rotation of the'clock in one direction and energization of the other causing its rotation in the reverse direction. The wires 105 and 104 lead to the relay G. As shown in the upper left hand corner of Figure 5, his relay is provided with an arm 107 which may be rocked in either direction from a central neutral position to which it is biased, to close connections between the wire 103 and either of thewires 104 and 105,which con nection being determined by a pair of solenoids 110, 111. .Each of these solenoids has one end connected to the wire 103 leading from the opposite power line 301 and each has its other end connected to one of the confields are independent, energization of one tact segments, solenoid 110 being thus con- 880 and is connected electrically to one side 300 of the power line. Thus, if when the needle. is depressed it is in mid-position,

neither of the solenoids 110 or 111 will be energized and the switch arm 107 will be in a neutral mid-position where it is yieldingly held and the motor 102 unenergized. If, when the needle is depressed electrical connection is made betwen the strips 860 and 870, the solenoid 110 is energized, thus closing the motor circuit through the wire 105 and causing the clock motor to rotate in a direction to turn the sector 850 to the left, this being done so long as the needle when in its depressed position bridges the" strips 860 and 870. lVhen the sector is moved sufiiciently to cause the needle when it is depressed to fail to contact. with the strip 860, the clock motor 102 becomes dc-energized and no further motion of the sector by this motor occurs. At the same timethat this motor .102 is energized, a controlling or adjusting mechanism of the valve-actuating mechanism H is operated to change the valve setting at-a speed proportional to that of motor 102 and ina correcting direction If the needle 50 should, when it is depressed, be on the opposite side of the central point of the sector 850 and so make electrical connection between the strips 860 and 880, solenoid 111 will be energized, thus closing the circuit through the wire 104, causing the motor 102 to rotate in the opposite direction and moving the sector 850 to the right, such action taking place as long'as the circuit is closed between the strips 860 and 880. At the same time the valve-actuating mechanism is operated in the reverse direction to effect a corresponding controlling action of the valve.

The valve-actuating mechanism, as herein showmmore particularly in Figures 1 to 4,

comprises'a constantly runnin motor which actuates through a suite lereducin gear, a crank disk-121l Thisis connecte by means of the connecting rod 122 to an arm 123, which is thus constantly rocked on a shaft 124 as a fulcrum. It carriesa pair of solenoids 125, 126. These solenoids are provided with cores .127 connected to an arm 128 fulcrumed at. 129 on the arm 123. Also 'fulcrumed at- 129 is a double pawl 130 normally held in' central position relative to the arm 128 as by mpans of the two leaf springs 131 engaging opposite faces of astem portion 132. Arm 128 is normally held in central position relative to solenoids and 126 as by coil springs. By energization of either of the solenoid magnets 125 and 126, the arm 12 8 may be rocked in either direction thus to bring one or the other end portions 134, 135 of the awl into operative'relation tda reversile'ratchet wheel 136 fixed to the shaft 124. The outer end of the solenoid 125 is connected to-the Wire 105 and the outer endpf the solenoid 126 tothe wire 104,- the inner end of these windings being connected together and to the line 300. When therelay G is operated to.

connect the'wire 103 tothe wire 105,-the so1e -Figures 3 and 4. .Referr-mg it will be seen that the shaft 124 carries at its and the end of the pawl is brought into operative relation, whereupon oscillation of the arm 123 rotates the ratchet wheel 136 in the opposite direction. The shaft 124 to which the ratchet wheel 136 is fixed extends outwardly of the casing of the apparatus H .and carries a sprocket Wheel 140 over which passes a chain 141, this chain leading about a sprocket wheel 142 (see Figure 1) journaled on a stub shaft at the end of a lever 143. On this lever rides a weight 144 which is connected to one side of the chain 141 so that on rotation of the shaft 124 in either direction the weight 144 is caused to move lengthwise of the lever 143. This lever 143 is shown as controlling a steam val e. The steam Valve is indicated at 145 and is shown as of the diaphragm controlled pressure regulating type, whereof the loading of the diaphragm and consequently the pressure that it wilhdetermine, is fixed by the position of the weight 144. The lever 143is shown as fulcrumed at on a bracket 156 carried by the exhaust pipe 157 so that .the position of the weight determinesthe load on the diaphragm. In accordance with a common practice this pressure regulating valve is shown as on the line leading from the paper machine engine to the engine and thereby determines the pressure and hence the temperature of the steam sup-.

ply through a branch pipe150 leading to drier cylinders of which one is'shown at 151. It.

will be understood, of course, that any other suitable mechanism for controlling the supply of the heating agent to the drier might be used it being only necessary that this supply 'should be controlled and in theright direction' in accordance with the action of the mechanism at E. r

In order that the weight 144 may 'not by anychance bemoved too far ineither direction on the lever, provision may be made by which the electrical connections for moving it in either direction will be interrupted when the weight is at the desired extent of travel in that direction. Such a me hanism is shown in to these figures,

upper end a threaded portion 160 on which rides a nut 161 held between a pair of jaws 162 atone end of one arm of a bell crank lever 163. The opposite arm of this bell crank lever hasfixed thereto a pair of switch ele.

ments 164 and 165, which, as shown, maypass between pairs of spring contact members 166 and 167,- respectively. The spring. contact members 166 are interposed inthe wire connection 105 and the spring contacts 167 are i one face of the bar 168 and is held in such position by any suitable spring means, but it may be swung away from bar 168 by pressure exerted thereon until the stop 171 on the opposite side of its pivot contacts with the base portion of the bar 168. Thus as either of these switch elements is moved out from between its corresponding spring contact aws, the member 170 is retained between the jaws while the member 168 passes therebeyond. When the portion 171 contacts with the lower part of the elements 168, so that no more pivotal motion is permitted, the switch element 170 snaps free from between the spring contact jaws as the bell crank lever 163 continues to move, springing back to its normal position against the bar 168. The parts are so designed, therefore, that whenever the solenoid 125 is actuated, the bell crank lever is moved gradually in a direction tending to break the connection between the spring contacts 166 and the element 164 and this occurs before the weight has been moved too far in its direction of sliding movement. Similarly the contact is broken in the wire connection 104 whenever the weight moves to its extreme position in the opposite direction.

It will be noted that the mechanism E is operatively connected to the valve controlling mechanism by electrical means. It is found in practice that where a direct unvari'able mechanical connection can not be conveniently used, as on account of inaccessibility of the valve, or for other reason, and an electrical mechanism is used, there is certain to be more or less deviation from exact synehronism between the operation of the mechanism E and the valve controlling mechanism, and as this lack of precise synchronism may be cumulative over long periods, in time any one setting of the instrument needle may not correspond to the same valve setting at which the mechanism was originally adjusted to operate, and consequently the moisture conditions which the mechanism may tend to maintain constant, are not those for which the mechanism was originally set.

While it isnot diflicult to reset the valve -mechanism by hand, as by throwing out the automatic control, as by means of the switch '180 (Figure 1), the relay mechanism being then actuated by hand as desired as by means of the knob 181 fixed to the pivot of the switch and means are therefore provided according to this invention by which there is a tendency .of the mechanism to re-establish periodically or concurrently with other editions an equilibrium relation between instrument-needle indication and valve-setting, and at the same time to bring the needle back to its initial setting for the desired moisture content on every departure therefrom quite regardless of What position the valve may occupy. For this purpose, as well as another which will later appear, as shown, the shaft 93, which is in alinement with the shaft 91, has fixed thereto a sprocket wheel 200 which is connected by a sprocket chain 201 to the drive sprocket of a reversible electric clock motor 202 similar to the clock motor 102. The wire 203 leading 1 from the common field point of this motor leads to the side 300 of the energy supply. The other field coil terminals 204 and 205 are connected respectively to the upper arcuate conducting strips 206 and 207 arranged back of the pivot point of the needle 50, ad'- jacent ends of these conducting strips being spaced apart as shown at 208. Spaced beneath the strips 206 and 207 is a continuous strip 209 insulated therefrom by. the supportin g block 210 in which these conducting strips are fixed. Between the upper and lower sectors rides a pin 211 carried by the sector 850. When the pin 211 is in its mid-position, this representing also the normal mid-position of the sector 850, the pin 211 rides on the strip 209, but is out of contact with both the strips 206 and 207. On the movement of the sector 850, however, through a lfollow-up motion.

occasioned by actuation of the motor 102, the

pin 208 makes electrical connection between one or the other of the stri s 206 and 207 and the continuous strip 209, t us energizing the motor 202, the strip 209 being shown as connected to the opposite side 301 of the current source from that of the wire 203. Operation of the motor 202 thus turns the shaft 93 in a the sector to its mid-position, This returning I tendency is exercised whether the depressor bar is down or up, whereas the follow-up motion is produced only when the depressor bar is down, since it is only at this time that the roller 56 is brought into electrical connection with the conducting strips 860 and 870 or 880 carried by the segment 850. Thls returning action of the motor 202 is thus accomplished irrespective of any follow-up motion, the ac- 1 tual resultant motion of the sector beingthe algebraic sum ofthe two at any instant. There is thusfno chance for the mechanism to come to equilibrium with the needle 50 ofi an... .c

center of the scale and at an undesired moisfture content, since it is always "returned when displaced therefrom in either direction whether ornot there is any resultant change in the setting ofthe steam valve.

The utility of the mechanism for returning the segment 850 relatively slowly to its mid position whenever displaced therefrom ma c more readily understood by certain detail considerations. The follow-up'motion which moves the sector 850 away from the central position in the dir'ectionof movement of the.

needle when theneedle is displaced from its central position would ordinarily bring about a new condition of equilibrium at a new position of the contacts 870 and 880 and conse I quently a new position of the needle 50 interwhich might be only mediate therebetween, and consequently, in turn, at a new equilibrium value of dryness a little removed from that desired, but WhlGhWOUld still not be ex actly-the predetermined dryness. This correction movement-which brings the contacts on the sector 850-back to the central position where deviation of the needle will .set up corrective actions in the drier, prevents any such equilibrium being established except at 4 predetermined dryness desired. This return to normal contact position may be. at a predetermined rate consonant with "the' rate at which in the circumstances the dryness can or should return to normal without entailing such heat storages or discharges in the drying parts as will cause the temperature correction of this part to overrumand set up fluctuations of dryness consequent thereupon. The rate of 'return can be controlled wholly or partly by rate of change of the driers or by the dryness of the paper or by time alone as may be desired. In'any event it is much slower than the follow-up movement. The time of return may be controlled by any suitable means such as by the use of changegears on the clock driving mechanism.

In paper machine regulation the rate of movement of the'sector 850 back to normal,

condition will usuall be intended to be correlated directely wit the rate at which the heav metal driers heat or cool when the heat.

supp y-to. them is cha ed. For example, suppose moisture norma at 7% changes to 7V %'and the instrunient needle 50 swings to the right by a corresponding amount causing the valve 145 to be operated, to increase the moisture of the'felt against which the paper passes, and'eventually if the 'valve be left unchanged, equilibrium will be reached at-7% moistureof the paper.

The proper speed of the motor 202 will then be thatat which the sector 850 will bebrought back toward the 7% mid-position just so fast that. -the mid-position of the sector will remain under the needle as the needle returns back to its 7% mid-position. In pointof fact a movement exactly meeting this requirement will not be a uniform one since the rate ofchange of drier temperature is faster at first than duringits stage of final approximation to its new temperature. However, a fair -mean value can be fixed upon that will serve all practical purposes and usually it is such that will bring the sector back to its proper mid-position at a time substantialy the same as or a little less thanthe temperature lag in the machine. 7 0

Not only does. this mechanism correct the departures from initial relationship between instrument and valve setting due to the drift previously defined between the valve and follow-up movement, since this accumulated driftis periodically canceled throu h reestablishment of a correct setting of t e aparatus, but it also prevents the apparatus rom assuming anew equilibrium point at a. Ynoisture content of the paper slightly difierent from thatdesired.

Having thus described this invention, together wlth certain mechanism by which the results sought ma be obtained, it should be evident to those s illed in the art that vari ous changes and modifications might be made withoutdeparting from the spirit or scope of thisinvention as defined by the appended claims.

I claim:

- 1. In a paper machine, a device responsive to the amount of certain constituents of the ,paper coming from such machine, means ac;

the heat andfmove the sector 850 with its cenj i' tral point opposite the new position of the needle. Suppose now that the new heat supply is just enoughto maintain equilibrium at 0 moisture under the new working conditions and therefore more than'enough to hold (I v.Atfirst the added heat will'go to heatingup the inner Eras of the driers and then to the outer wor g surfaces and will- 7 increase the drying of'the -p'aper,.cut down means for controlling said mechanism, a device responsive to moistureof material delivered from said mechanism, means controlled byvariations of response of said device from that response indicating a desired normal moisture content of said material for actuating said controlling .mechanism, and means tending to return'said actuating means when displaced therefrom to a condition corresponding to the response of such device to compared with the timeof such displacement.

normal moisture of said material.

3. In a paper machine, aidevice IOSPOI'ISIVCJ 'to the amount of certain constituents of paper coming from such machine, means, actuable to vary the amount of such constituents, means rendered periodically Operative for actuating said varying means in corrective dircction when the response of such device is different from the response due to a normal desired amount of such constituent, and means tending-t0 return said actuating n'iearisv when displaced therefrom to its condition corresponding to normal response of said device to the desired amount of such constituents.

4. In combination, a drier, a. valve for controlling the supply of a drying'agent to said drier, a device responsive to moisture content of material coming from said drier, means controlled by variations in the response of said device from that indicating a desired normal moisture content of such material to change the opening of said valve in a correcting' direction, and means tending on each displacement therefrom to return said changing means to its condition corresponding to 'normal response of said device to the desired moisture content and to complete such return only after a time interval large compared with the time of such displacement.

5. In a paper machine, means actuable to vary the amount. of certain constituents of paper coming from said machine, a device responsive to the amount of such constituents, means controlled by variations. in the response of said device from that indicating a desired normal amount of such constituents to actuate said varying means in a corrective direction, and means tending on each displacement therefrom to return said actuating means to its condition corresponding to normal response of said device to the desired amount of said constituents and to complete radii No, 1,722,655. V

. E RT CERTIFICATE or oonimc'nou.

i r i such return only after a time interval large 6. In combination, drying mechanism, a device responsive to moisture content of material coming from'said mechanism, means for varying the drying effect of said mechame'chanism, sai'd controlling means having a movable element the position of which is controlled by the response of said device and follow-up means relative to which said device moves, means for actuating said varying means in correcting direction on departure of said element from a determined point of said follow-up means, means actuable on each such departure to move said follow-up means in a direction to bring said point toward said element, and means acting during a. period longer than that of the movement of said follow-up moving means to return said follow-up means to a central position where said point represents an element position corresponding to the desired moisture content of the material.

7. In a mechanism for controlling the moisture content of material coming from a drier in which deviation of moisture content from that desired causes movement of an element from a normal position relative to a follow-up member, such movement relative to said member changing the rate of supply of adrying agent to the drier and causing move ment of said member toward said element to cause the amount'of rateIchange to be proportional to the extent of departure of the moisture from the desired amount, that stepwhich comprises moving said member on deviation in either direction from a central .normal nism, means for controlling said varying position toward said central normal position signature.

HERBERT. L. BONE.

Granted July so, 1929, a

BONE.

'It is herebycettliiid that the assignec in the above numbered patent was erroneously described and specified as "Atlantic Precision G0l! 1P ll Y :hel cfl said nan'ie should havcheen'dcacribcd and specified as; "AtlaHtFf- PIFCIBIOP instruiiientflompany", as shown by the records of" assignments m this office; and that the said Letters. Patent should be read gvith this correction therein that the same may conform to the-record 0t thc'casc in the Patent Office.

' Siihed and lcaled'thic ZQth ddy' ofrAuzuotr Ire M; 'J. -Moor'e,": I Acting Gonmis'aioner of Patents.- 

